1. Field of the Invention
The present invention relates generally to the purification of contaminated liquids and more particularly to the methods and apparatus for electrochemical purification of contaminated liquids.
The invention may be employed for purifying a liquid contaminated with organic substances, mechanical suspensions, surfactants, and the like. The invention is particularly useful for purifying liquids contaminated with polymers and petroleum products, such as waste water containing oils and fats.
2. Description of the Prior Art
Of all the prior art methods for purifying contaminated liquids, the widest and ever increasing application have recently found methods of electrochemical purification of liquids, such as electroflotation and electroagulation methods due to their high performance capabilities. Known in the art are methods of electrochemical purification of liquids wherein the process of purification is accomplished either discretely or continuously. The latter methods are considered to be more promising.
In a method disclosed in the description of operation of an apparatus for electrochemical purification of contaminated liquids (USSR Inventor's Certificate No. 407,844), the electrochemical purification of contaminated liquids is accomplished by mixing the latter within an electrocoagulation chamber in the space between and above the electrodes with products of dissolution of the electrodes followed by separating formed foam and sludge from the purified liquid within a settling chamber. An apparatus for practicing the above method (disclosed in the above-mentioned Inventor's Certificate) comprises a settling chamber which houses an electrocoagulation chamber and communicates with the latter, and a system of soluble electrodes disposed in the bottom portion thereof. The electrocoagulation chamber comprises an inlet pipe to feed contaminated liquid, disposed beneath the soluble electrodes, while the settling chamber comprises an outlet pipe to discharge purified liquid. In the course of purification, contaminated liquid containing electrolyzing additives (hydrochloric acid, sodium chloride) passes through the soluble electrodes whereto electric current is applied. This brings about the formation of hydroxides of the soluble electrode metal, which hydroxides coagulate impurities contained in the liquid being purified. From the electrocoagulation chamber, said liquid passes into the settling chamber where foam and sludge separate from the liquid, following which the foam, the sludge, and the purified liquid are discharged separately. When passing through the electrodes, the liquid being purified fouls these, which accelerates passivation of the electrodes and, hence, increases the power consumption and necessitates frequent cleaning of the electrodes, i.e. eventually reduces the efficiency of the apparatus.
Known in the art are a method and an apparatus for electrochemical purification of contaminated liquids (Japanese Pat. No. 52-143,973, published Nov. 30, 1977), characterized in that the electrocoagulation chamber serves only to produce coagulants, for which purpose clean electrolyte is fed thereinto, while liquid purification is accomplished in another chamber whereinto the liquid to be purified is fed and wherein the liquid is mixed with the electrolyte containing coagulants and being fed from the electrocoagulation chamber. While greatly diminishing the fouling of the electrode surfaces, the above process and apparatus considerably less utilize the coagulation and flotation capabilities of the electrodes, since when the electrolyte passes from the electrocoagulation chamber to the settling chamber, the coagulants (hydroxides of the soluble electrode metal) and gas bubbles forming on the soluble electrode surface aggregate, which reduces their specific surface and hence impairs the coagulating and flotating capabilities. The above factors adversely affect the apparatus efficiency. Moreover, to install such an apparatus, larger areas are required than for the apparatus of similar efficiency, disclosed in USSR Inventor's Certificate No. 407,844.
Also known in the art are methods and apparatus for electrochemical purification of liquids, characterized in that contaminated liquid is fed into an electrocoagulation chamber through an inlet pipe disposed above the soluble electrodes, while the clean electrolyte is passed in an ascending flow between the electrodes. Mixing the contaminated liquid with products of dissolution of the electrodes is accomplished only in the space above the electrodes. This method and the apparatus for practicing thereof are characterized in that the purification of liquids is accomplished with essentially no fouling of the electrodes and a lesser deterioration of their coagulation and flotation capabilities. The efficiency of the above described method and apparatus is higher than of those disclosed in Japanese Pat. No. 52-143,973.
For example, a method known from the description of operation of an apparatus for electrochemical purification of contaminated liquids (USSR Inventor's Certificate No. 644,738) comprises mixing contaminated liquid within an electrocoagulation chamber above soluble electrodes with an ascending flow of electrolyte containing products of dissolution of the electrodes, followed by separating formed foam and sludge from the purified liquid within a settling chamber.
The aparatus for practicing the above method (disclosed in the above-mentioned Inventor's Certificate) comprises a settling chamber communicated by means of a recirculation pipe with an electrocoagulation chamber disposed therewithin and provided in a bottom portion thereof with a system of soluble electrodes, an inlet pipe to feed a contaminated liquid into the electrocoagulation chamber, and an outlet pipe to discharge the purified liquid from the settling chamber. The inlet pipe to feed the contaminated liquid into the electrocoagulation chamber is disposed above the soluble electrodes. The inlet pipe should be spaced from the electrodes at such a distance which excludes the possibility of fouling the surfaces of the soluble electrodes in the course of purification. Thus, when the inlet pipe is of a cylindrical configuration, the distance should be of (1 to 7)d, where d is a diameter of the inlet pipe.
The main disadvantage of the above described process consists in that an intensive aggregation of coagulants and gas bubbles occurs within the electrocoagulation chamber between the inlet pipe to feed the contaminated liquid and the soluble electrodes, which aggregation is caused by the turbulization of the electrolyte flows. At the same time, the reduction of the distance between the inlet pipe and the electrodes leads to the fouling of the latter, which fouling is rather undesirable. This disadvantage limits capabilities of both the above described apparatus and the method practiced thereby.